There are four ways to collimate a reflector and they cost between almost nothing and about the price of a good eyepiece. All four work; they differ in speed, precision and in how confidently they can mislead you when something is wrong.
Which telescope do I need? Ask us below
The collimation cap
A lens cap with a small central hole. It costs almost nothing and makes one thing visible: whether the reflections you see are concentric. For the secondary mirror it is genuinely sufficient, and for the primary it gets you close enough that a star test finishes the job. Every reflector owner should have one before buying anything else.
The cheshire eyepiece
A cap with a crosshair and an illuminated face, so you can see both the reflections and a reference to line them up against. Slower than a laser and more trustworthy, because there is nothing in it that can itself be out of alignment. Many experienced observers use nothing else.
The laser collimator
Fast, works alone in the dark, and carries one real hazard: a laser that is not itself collimated will confidently point your mirrors at the wrong place. Roll it in the focuser and watch whether the dot moves in a circle. If it does, the tool needs adjusting before it can align anything else.
The star test, which settles arguments
Point at a bright star at high magnification and defocus slightly. The rings should be concentric. If they are lopsided in the same direction whatever tool you used indoors, the tool was wrong. This is the only test done through the whole optical path at the working temperature, and it is the one that decides.
Questions people ask about collimation
Which telescope collimation tools do I need?
A collimation cap is enough to start and costs almost nothing. A cheshire adds precision; a laser adds speed and needs checking itself.
Is a laser collimator accurate?
Only if the laser itself is collimated. Roll it in the focuser and watch the dot: if it circles, adjust the laser before trusting it on your mirrors.
What is a collimation cap?
A simple cap with a central hole that lets you see whether the mirror reflections are concentric. It is the cheapest and most reliable starting tool.
Collimation cap vs cheshire: which is better?
The cheshire is more precise, because its crosshair and illuminated face give you a reference to line the reflections up against, where the cap only shows whether they are concentric. The cap costs almost nothing and is enough for the secondary mirror, so start with it and add a cheshire when you want the extra precision.